Electron valve with centered heater



Jan. 10, 1933. s. LOEWE ET AL ELECTRON VALVE WITH CENTERED HEATER Filed Aug. 25, 1928 Patented Jan. 10, 1933 UNITED STATES PATENT OFFICE ELECTRON VALVE WITH CENTERED HEATER Application filed August 25, 1928, Serial No. 301,965, and in Germany August 31, 1927.

The invention relates to a centering device, especially in electron valves, which. is of advantage under difficult conditions.

In the case of several kinds of electron valves, especially such with equipotential cathodes which are indirectly heated, the heating wire is surrounded by so thin a cylindrical tube that a centering of the wire in the tube can only be effected with difficulty.

Special difficulties arise for the transport of the tubes and more particularly for such tubes which are to be kept working during a movement (possibly during a mechanical natural vibration provoked by an external shock). With such electron valves there exists a definite maximum temperature for the heater which depends on its strength and generally does not exceed 2000. There exists on the other hand for the cathode surrounding the heating wire a minimum temperature of the cathode surface depending on the material of the cathode surface which always according to the emitting electrodematerial in many cases is not below 250, wh1ch, however, frequently takes the order of magnitude of the temperature of the heater. Wlth such arrangements the internal diameter of the cathode tube is within narrow limits established by the electrode materialand the manner of heating. If, more particularly cathodes heated by alternating current are concerned, the heating wirein order to obtain a good heat inertia is selected of not toosmall a diameter. In this manner the margin between the surface of the heater and the inside of the cathode tube is only very small,

With an exemplary embodiment, for in stance, the diameter of the heater was 0.2 mm and the internal diameter of the surrounding tube (equipotential cathode) 0.6 mm. Such a small distance of 0.2 mm between the inner wall of the cathode tube and the surface of the heater is necessary, if the cathode merely by heat radiation is to be brought to a temperature little below the temperature of the heater.

The conditions are similar with such narrow cathode tubes surrounding a heater which by electron bombardment are to be brought to a temperature even higher than the temperature of the heating wire.

The arrangement of a wire in a cylindrical tube in such manner that in all directions a constant distance of only 0.2 mm remains, is more particularly diiticult if by heating changes in the shape of some of the parts concerned are to be expected. In the present case therefore the centering process hitherto usual under similar conditions, had to be abandoned. It has been suggested that a constant distance may be obtained if the heating Wire is surrounded by a tube of insulating material. This means a renunciation of some of the heating processes possi- 6 ble for the present purposes, since with interposition of an insulating jacket more or less conducting the heat, the heat transmission by radiation considerably recedes. The heating by electron bombardment remains hardly possible.

By the invention these disadvantages are avoided. For this purpose according to the invention merely an insulating ring is inserted at some places of the heating wire, especially at its two ends, which does in no manner impair either the heat radiation or the electron course over the main length of the heater which, however, with especially good centric finish may exercise at least the same centering effect as an insulating tube. In this respect it should be particularly considered that an insulating tube which is to be introduced into the inside of the cathode tube to be insulated and into the inside of which a wire is to be coaxially inserted, may in view of the inexactitudes in the cylinder symmetry not be executed of so firm a fit as the two insulating rings according to the invention which are to be arranged at the ends of the tubes.

It has further been discovered that this manner of carrying the invention into practice on a small scale still suffers certain defects which with the use of insulating tubes occur on a large scale. With the temperatures in question for the heating Wires and the tubes to be heated most insulating substances useful for such purposes (such as clays, magnesium-oxide containing substances, quartz, porcelain and other ceramic substances, further glass too) prove to be rather bad insulators. This fact is also noticeable to a certain degree with the comparatively small cross-sections in question for the heat circuit, since more particularly with heating wires connected with a fluctuating potential of E. M. F. (especially with wires heating by alternating current) a special advantage of the indirect heating may be achieved if it is possible to well insulate the heater from the cathode and in its manner to make the cathode independent of the variations in the a. c. voltages.

This is made perfectly possible by the further subject of the invention. For this purpose the insulator is not arranged in the immediate proximity of the hot elements, but taken to a distant point of such temperature with which the insulating resistance of the material concerned still possesses a sufficiently high value. This is preferably eifected in the manner that the insulation material possesses a larger diameter than the cathode tube in order to increase the heat radiating off surface and for reducing the temperature of the insulation material.

The invention may be best understood with reference to the accompanying drawing, the figures of which illustrate an exemplary embodiment of the invention.

Fig. 1 shows a section of an electron tube with the cathode according to the invention.

Fig. 2 illustrates another form of the centering device for the heater of an indirectly heated cathode.

Fig. 3 shows the face of the centering device on a larger scale.

By means of Fig. l the manner is illustrated in which the centering of the cathode as per Fig. 2 is produced.

In Fig. 1 there is 1 the heating wire, 2 a cathode, 3 the above mentioned plugs of insulating material according to the first embodiment of the invention. T he other parts of the electron tube are drawn in a well known manner.

In Fig. 2 a further embodiment of the invention is illustrated. In such embodiment the heater 1 is provided with a ring 5 supported in the form of rays. In similar manner the cathode cylinder is provided with a ring 7 supported by similar spokes 6. Between the two rings 5 and 7 a mica disc 8 is clamped which is thus held by the rings 5 and 7 that its inner edge 9 does not touch the heater.

Fig. 3 discloses the execution of such centering device, looked upon from the side on a larger scale. It shows at the same time that the spokes 4 and 6 for the two holding rings do not lie opposite one another. The extensions of the spokes grip round the insulating wire and thus favour a good support.

How the heater 1 of the cathode 2 according to Fig. 2 may be centered will be described with reference to Fig. 4. Firstly to the c lindrically shaped cathode 2, which may e made of nickel or an alloy of nickel, a plate 4, 5 is welded on one side, say at the right side. For this purpose the plate 4, 5 may be made of the same material of which the cathodic cylinder is made. Then the elongations of the spokes 4 of the ring 5 are turned in such a way as to fasten it to the insulating ring 8. Afterwards a plate 6, 7 is fastened on the right side of the cathode to the other side of the same insulating plate 8 in the" same manner. After fastening in such a way to one side of the cathodes 2 the two metallic plates 4, 5 and 6, 7, the insulating plate 8, and a thorn 11 is introduced in the interior from the open side, that is to say from the left to the right. It is important that the diameter of the thorn 11 is as great as the interior diameter of the cathodio cylinder. t

As may be seen from Fig. 4 the thorn 11 has a small point to the right side of the same diameter as the hole shall have, which is to be made to the plate 7. This hole is made by sticking or drilling the thorn 11 through the middle part of the ring 7 from the interior 2 until the thorn 11 has the situation as indicated at the right side of Fig.4: by means of dotted lines. In such a way the whole inner surface of the cathodic cylinder is used as centering surface and therefore centering maybe made most exactly.

The temperature conditions with such embodiment of the invention may, for instance, be as follows: The wire may be at a temperature of 2000, thecathode having a temperature of 700. The main insulating task is entrusted to the outer portion 10 of the mica disc. Such outer portion is from the side of wire 1 and of tube 2 connected only by the long paths of the spokes 4; and 6, respectively. It is therefore at so low a temperature that the insulating resistance is still agood one and that the crystalline properties of the mica also do not undergo any disturbing changes. Even if the inner edge 9 owing to the proximity of the heater should reach a higher temperature, the properties of this point do not impair the insulating power. By the spokes 4 and 6 being displaced against one another, a further advantage of the arrangement is accomplished both regarding the heat transition and in electric respects.

We claim:

1. In an electron discharge device an indirectly heated cathode consisting of a heater element, a cylindrical metallic cathode tube surrounding said heater element, a metallic body mounted on each end of the heater element, a metallic body mounted on each end of the cathode tube and two insulating bodies, each arranged between one of said first mentioned metallic bodies and one of said second mentioned metallic bodies.

2. In an electron discharge device an indirectly heated cathode consisting of a heater element, a cylindrical metallic cathode tube surrounding said heater element, a metallic body mounted on each end of the heater element, a metallic body mounted on each end of the cathode tube and two discs of insulating material, each arranged between one of said first mentioned metallic bodies and one of said second mentioned metallic bodies.

3. In an electron discharge device an indirectly heated cathode consisting of a heater element, a cylindrical metallic cathode tube surrounding said heater element a metallic disc mounted on each end of the heater element and being provided with a ring supported by radial spokes, a metallic body mounted on each end of the cathode tube and two insulating bodies, each arranged between one of said metallic discs and one of said metallic bodies.

4. In an electron discharge device an indirectly heated cathode consisting of a heater element, a cylindrical metallic cathode tube surrounding said heater element, a metallic disc mounted on each end of the heater element and being provided with a ring supported by radial spokes, a metallic disc member mounted on each end of the cathode tube and being provided with a ring supported by radial spokes and two insulating bodies, each arranged between one of said discs and one of said disc members.

5. In an electron discharge device an indirectly heated cathode consisting of a heater element, a cylindrical metallic cathode tube surrounding said heater element, a metallic disc mounted on each end of the heater element and being provided with a ring supported by radial spokes, a metallic disc member mounted on each end of the cathode tube and being provided with a ring supported by radial spokes, and two discs of insulating material, each disc being clamped between the spokes of one of said first mentioned discs and the spokes of one of said second mentioned discs.

6. In an electron discharge device an indirectly heated cathode consisting of a heater element, a cylindrical metallic cathode tube surrounding said heater element, a metallic disc mounted on each end of the heater element and being provided with a ring supported by radial spokes, a metallic disc member mounted on each end of the cathode tube and being provided with a ring supported by radial spokes, and two mica discs, each mica disc being clamped between the spokes of one of said first mentioned discs and the spokes of one of said second mentioned discs.

7. In an electron discharge device an indirectly heated cathode consisting of a heater element, a cylindrical metallic cathode tube signatures.

SIEGMUN D LOEWE. EDGAR RCjMHILD. 

